1. Field of the Invention
This invention relates to a process for producing an olefin polymer small in the content of fish-eye (the gel deteriorating the appearance of product processed and made into an article), high in bulk density, small in the content of fine powder and good in fluidity by using a solid catalyst component having a very high activity per transition metal in the gas phase polymerization process.
2. Description of the Related Art
Highness of the activity, particularly the activity per transition metal, of a catalyst (the quantity of polymer formed per unit quantity of catalyst) used in the production of olefin polymers is quite valuable industrially because such a catalyst makes it unnecessary to remove the catalyst residue from the polymer obtained by polymerization and can thereby simplify the production process. On the other hand, smallness in the extent of adhesion of formed polymer to polymerization reactor, highness in the bulk density of polymer powder, narrowness in the particle size distribution of polymer powder and goodness in the fluidity of polymer powder are desirable from the viewpoint of stability and efficiency of operation. From the viewpoint of quality of product, as small a number of fish-eye as possible is desired because it deteriorates the appearance and properties of processed articles.
In the recent years, a number of reports have been published concerning the fact that a solid catalyst component comprising a magnesium compound and a titanium compound can function as an excellent high-activity polymerization catalyst for olefins (for example, Japanese Patent Application KOKOKU Nos. 50-30102, 57-24361, Japanese Patent Application KOKAI No. 61-296007, etc.). However, if an olefin is polymerized in gas phase by using these high-activity Ziegler catalysts, a large quantity of heat is generated at the time of polymerization which makes the resulting polymer into a bulky mass and makes difficult the progress of polymerization.
As a method for preventing the formation of bulky polymer, methods which comprise preliminarily polymerizing ethylene and/or .alpha.-olefin and thereafter polymerizing olefin in gas phase is known (for example, Japanese Patent Application KOKAI Nos. 48-45284, 59-30806, Japanese Patent Application KOKOKU Nos. 52-45749, 60-26407, 61-9964, 64-10532, Japanese Patent Application KOHYO No. 61-502061, etc.). However, these methods are yet unsatisfactory in the particle characteristics of the resulting powdery polymer.
On the other hand, with the aim of improving the particle characteristics of the resulting powdery polymer, there have been disclosed methods which comprise impregnating a porous inorganic carrier with catalyst components (for example, Japanese Patent Application KOKOKU No. 61-26805, Japanese Patent Application KOKAI Nos. 56-24409, 58-179209, etc.). However, it cannot be said that a polymer powder good in fluidity and high in bulk density or a polymer giving a molded film small in the content of fish-eye can be obtained by these methods.
With the aim of solving these problems, there have been disclosed methods which comprise impregnating a porous carrier with catalyst components and preliminarily polymerizing ethylene thereon (for example, Japanese Patent Application KOKAI Nos. 61-87703, 64-16804, 1-261404, 3-72509, etc.). However, these methods are yet unsatisfactory in the points of particle characteristics and fish-eye.
Apart from the above, there are known methods of preliminarily polymerizing an .alpha.-olefin (for example, Japanese Patent Application KOKOKU No. 63-46084, Japanese Patent Application KOKAI Nos. 59-184207, 2-51505, etc.). However, these methods are undesirable because they have a problem concerning the adhesion of polymer powder to the preliminary polymerization-reactor, etc.